In some studies, no differences were found in the expression of AQP4 in the frontal cortex between AD patients and controls (Rodriguez et al., 2006; Perez et al., 2007), while one study reported that the expression of AQP4 was significantly decreased in stage IV–V AD patients with moderate or severe cerebral amyloid angiopathy (Moftakhar et al., 2010). Here, AQP4 is linked to Alzheimer disease.